1. Field of the Invention
The present invention relates to a process for preparing N-alkyllactams from lactams and alkyl halides.
2. Discussion of the Background
N-alkyllactams are compounds which are known from the literature (Houben-Weyl, Methoden der Organ. Chemie (Methods of Organic Chemistry), G. Thieme Verlag Stuttgart, Vol. XI/2, p. 568).
The most frequently used preparation method is to react a lactam with metallic sodium or NaH in xylene or benzene and to further react the resulting product with an alkyl halide or alkyl sulfate to give the N-alkyllactam. Thus, A. P. Swain et al. (J. Org. Chemistry, vol. 18, p. 1087 (1953)) prepared N-hexadecylcaprolactam and other N-alkylcaprolactams in a reported yield of 62% by boiling in xylene for 40 hours. In this manner, C. S. Marvel and W. W. Moyer (J. Org. Chemistry, vol. 22, p. 1065 (1957)) achieved yields of 63-78% for various N-alkylcaprolactams. By exactly the same method, T. Duong et al. (Austr. J. Chem., vol. 29, p. 2651 (1976)) prepared seven further N-alkyllactams using NaH in benzene as the condensation medium.
However, the handling of metallic sodium or NaH and the use of carcinogenic solvents is associated with higher risks. Moreover, the reported yields of these methods are not yet satisfactory.
The condensation of lactams with alkyl halides in aqueous systems using NaOH with phase transfer catalysis has also been described. J. Palecek and J. Kuthan (Z. Chemie, vol. 17, p. 260 (1977)) report that the yields decrease with increasing ring size of the lactam and increasing C number of the alkyl bromide; the yields obtained are 15-73%. U.S. Pat. No. 4,380,162 reports that when using the PT catalyst tetrabutylammonium hydrogen sulfate reaction times of 114 hours are necessary for achieving yields of &gt;90% of N-dodecylcaprolactam. Such long reaction times are uneconomical, traces of sulfur frequently interfere in the subsequent reactions, and the disposal of the aqueous chlorocarbon-containing phase also presents a problem.
Other preparation methods include the condensation of lactones with alkylamines at elevated temperatures of about 275.degree. C. and pressures of up to 33 bar with elimination of water (PCT Int. Appl. WO 8800 184) or the cyclization of .omega.-alkylaminocarboxylic acids at about 230.degree. C. with elimination of H.sub.2 O (DE-A 3,735,904). The ring closure of .omega.-dialkylaminocarboxylic acids with phosphoric acid chlorides at elevated temperatures has also been described (U.S. Pat. Nos. 4,310,948 and 3,588,248). All these methods comprise several complicated synthetic steps.
Thus, there remains a need for a process of preparing N-alkyllactams which is environmentally friendly and affords the desired N-alkyllactam in high yield and high purity.